The invention relates to a method for the hardening of camshafts wherein the cams of the camshaft are hardened simultaneously in groups while the camshaft is rotating, and wherein during the inductively performed heating of a group the zone of the camshaft that is not to be hardened and bordering on the group concerned is shielded from heating by means of a cooling device. In addition, the invention relates to a linear inductor intended to perform the method.
A basic problem in the hardening of closely proximate hardening zones of a camshaft is that the heating of an individual cam can cause the supplementary tempering of the previously hardened and directly proximate cam. When hardening is being performed individually, therefore, it is necessary to shield the cams bordering on the cam being treated. The requisite expenditure on apparatus for this purpose is substantial. Moreover, the hardening of cams individually implies a considerable duration in the processing time required for the hardening of a shaft.
For the purpose of shortening the processing time and eliminating the problem of the additional tempering of previously hardened and directly proximate cams, it has been proposed in the special issue of "elektrowarme international", number 3/75, "Induktionshartetechnik fur Nockenwellen von Verbrennungsmotoren [induction-hardening technique for camshafts of combustion engines]" that the cams of a camshaft be combined into groups and that the cams of one of these groups at a time be hardened simultaneously. The size of the group and the length of the group are determined by the distance to those zones of the camshaft that should not undergo any hardening. This process permitted a substantial shortening in the processing time required for the hardening of a camshaft. Furthermore, due to the simultaneously effected heating of the closely proximate cams, the problem of the supplementary tempering of previously hardened cams no longer exists.
The requisite expenditure on apparatus for the simultaneous hardening of a group is still substantial even with the process explained above, since an individual inductor, riding as a rule on the cam involved, is used for each cam. For the purpose of reducing this technical expenditure, it has been proposed that the camshaft be hardened by means of a linear inductor extending along the camshaft and positioned in the area of the envelope curve of the camshaft (DE-GM 75 27 498). It has turned out, however, that the use of such a fixed inductor, because of the varying coupling distances in a camshaft rotation, causes overheating of the tips of the cams or insufficient heating of the other sections of the cam being processed.
On the basis of the state of the art explained above, the task of the invention is to provide an economically practicable process for the hardening of camshafts and a particularly suitable inductor for performing the process.